1. Field of the Invention
The present invention relates to image processing apparatus and method which use a recording method based on area gradation and a recording method for performing visual smoothing.
2. Related Background Art
In recent years, office automation (OA) apparatuses such as a personal computer, a word processor and the like have been widely used, and apparatuses of a number of systems have been also developed as apparatuses to print out image information and the like inputted by these OA apparatuses. In these apparatuses, a recording apparatus of a dot matrix system such as an inkjet system, a wire dot system, a thermal system or the like is the recording apparatus of a digital recording system which is most used at present, because this apparatus is relatively cheap and can be easily made compact in size.
In the recording apparatus of the digital recording system, since analog gradation expressing is difficult in unit of dot, a pseud halftone is expressed in an area where a plurality of dots cover a paper surface.
Further, in image forming by the recording apparatus of the dot matrix system, since an image is formed by combining the dots with others, image quality is sometimes deteriorated because an indention (or sawtooth) phenomenon occurs in a contour such as an oblique line portion of the image. In the part of the recording apparatus of the dot matrix system which intends to perform extremely high-quality outputting, a countermeasure to relieve the indention phenomenon is provided as shown in Japanese Patent Application Laid-Open No. 2-112966. That is, in order to relieve the sawtooth phenomenon, a plurality kinds of matching detection patterns of (n.times.m) pixel size which are used to detect an indention portion and have been already set are compared with an original image. Then, to a portion of the original image at which the original image coincides with the matching detection pattern, an interpolating process is performed in accordance with a rule inherently set for such the matching detection pattern.
However, in the conventional interpolating process of the original image for relieving the indention phenomenon, since it is necessary to newly provide interpolating pixel data (i.e., matching detection pattern), a capacity of a memory increases, whereby it occurs problems that a cost increases and a processing time prolongs.
Further, if multi-gradation input image data is quantized into ternary or more data, it is very difficult to improve gradation (or tonality) by expressing the halftone of one pixel with use of the plurality of dots of which hit positions are different from others and simultaneously to suppress the indention phenomenon on the contour of the image. Namely, the gradation can be improved by quantizing the multi-gradation input image data into the ternary or more data, but such the quantizing does not at all affect the indention phenomenon on the contour and thus does not improve resolution.